1. Field of Invention
This invention relates generally to trocar systems and more specifically to obturator apparatus and methods for placing a trocar cannula across a body wall.
2. Discussion of the Prior Art and Related Technology
It is generally well known that holes can be created through body tissue either by cutting the tissue or by mechanically parting the tissue along lines of weakness. Where tissue is cut, it is severed along a line, which is determined by the direction of the cutting implement. Where tissue is parted, it separates along natural tissue planes such as those defined by muscle fibers or differing layers of tissue such as skin and muscle. Tissue that is mechanically separated tends to heal better than tissue that is cut with tissue that is mechanically separated the healing process requires only that the affected tissues re-approximate each other with cut tissue, and in particular muscle fibers, the healing process must reconstruct the damaged tissue, often with resultant scaring and incomplete reconstruction. It has been shown for laparoscopic surgery in particular, that trocar wound sites of 10 millimeters in diameter and higher, made by cutting obturators, require suturing to prevent incisional hernias from occurring. It has also been shown that where the same size would site is created by expanding or parting the wound from a cut of 3 millimeters, for example, that the wound site does not require stitching and tends to heal faster.
For laparoscopic surgery there is a requirement that instrument ports in the form of cannulas be placed in the patient's abdominal wall. These cannulas are then used as access ports for the surgeon to place instruments such as scissors and graspers. In the past these cannulas have been introduced by using a sharp cutting obturator, placed within the cannula, to cut a line or hole for advancing the cannula through the abdominal wall. The obturator is then removed from the cannula and the cannula is left in place for the duration of the surgery.
For most surgeries the cutting obturator is only used after the abdomen has been insufflated with carbon dioxide gas. There is then separation between the abdominal wall and the underlying anatomical structures and organs. Even with this separation, however, there is a risk that the patient will be injured by the sharp cutting tip of the obturator as it breaks through the abdominal wall. To help resolve this issue a variety of mechanical shielding mechanisms have been employed to cover the cutting element once it breaks through the abdominal wall. It has been noted and observed that even with these mechanical shield mechanisms that the risk is not completely eliminated and that the rigid shields themselves can cause damage to internal organs and structures.
Other methods have been used as well. For example, optical trocars have been provided with a clear plastic cutting tip. This allows the surgeon to view the tissue layers as they are cut, and in principle to better control the timing of insertion forces. These plastic tips, however, are not as sharp as the metal bladed variety and therefore require a higher insertion force which in turn increase abdominal wall distortion. This distortion or tenting brings the obturator tip into closer proximity with the internal organs and increases the chances for potential damage. The wound created by such a device is still a cut and not a mechanical separation, as it still suffers from the above-mentioned disadvantages.
Another manufacturer employs a multistage system whereby a sheath is inserted over a veress needle. The needle is then removed and a conical obturator, placed inside a cannula, is inserted through the sheath thereby expanding it to the desired cannula size. The obturator is then removed leaving the cannula in place. This offers the advantage of a smaller initial incision with the veress needle. However, the needle still presents a risk to internal organs, and the system is more expensive and complex than those associated with the cutting obturator devices.
In all of these systems of the past, a cutting element is employed to either create the final size of the wound site or to make a smaller initial wound site that is then expanded to the final size. The use of sharp cutting elements common to all systems presents an unavoidable risk to the patient.